The overall aims of the subproject involve the use of microdissection and microcloning techniques to construct region-specific microdissection libraries of chromosome 21 for high resolution molecular analysis of Down syndrome phenotypes and for isolation of expressed gene sequences from chromosome 21. These studies will provide direct link between cytogenetic and molecular levels of resolution of chromosome 21 and should facilitate search for genes responsible for specific component phenotypes of Down syndrome (DS). The specific objectives are: (1) Construction of sub-region microdissection libraries of chromosome 21 for isolation and characterization of region-specific microclones, and (2) isolation and characterization of region-specific expressed sequences from chromosome 21. A microdissection and microcloning technology developed under this program project will be used to construct libraries for chromosome 21 regions including 21pter-cen, 21cen-q21 and 21q22. Special bacterial host strains will be used for a more complete representation of genomic sequences in the library, particularly for the proximal long arm region 21q21 where probes are deficient. Unique sequence microclones will be isolated from these libraries and characterized for use in isolation of corresponding YAC clones with large inserts. These chromosome 21 region-specific libraries will also be used for the FISH painting analysis of DS with apparently normal karyotype. The unique sequence microclones from chromosome 21 will be used for isolation of cDNA clones by direct screening of cDNA libraries and by the immobilized filter hybridization procedure. Large scale isolation of as many cDNA clones as possible from chromosome 21 will be carried out and the isolated cDNA clones will be characterized, regionally assigned and sequenced. These region-specific cDNA clones will be studied for involvement in DS individuals with partial trisomy to determine possible causal relationships with specific component phenotypes of DS.